The first interest in thixotropic gelled propellants was aroused by their obvious advantages of increased safety, reduced sloshing, and ease of pumping at zero gravity conditions. Thixotropic gels also have the ability to stabilize high concentrations of metals or high-energy powdered ingredients in a uniform suspension while still providing the capability to be pumped, injected, and burned as a normal liquid propellant. The incorporation of high-energy ingredients in the gels provides compositions offering the potential of both high Isp and high density Isp which translates to significant increases in total system performance.
An Army program was initiated to develop a gelled fuel to capitalize on these advantages. MICOM GEL, which is a high density, high energy, gel formulation, was developed and has undergone extensive laboratory testing. MICOM GEL has been fired in a LANCE engine system using ungelled Inhibited Red Fuming Nitric Acid (IRFNA) as the oxidizer. All the laboratory and engine test results of MICOM GEL were highly satisfactory. One of the primary reasons MICOM GEL was developed was to provide the Army with a thixotropic gel possessing rheological properties which would permit it to be used within Army environmental limits (-65.degree. F. to +165.degree. F.). The rheological properties of MICOM GEL were shown to be better than previously developed thixotropic gels. However, the viscosity of all thixotropic gels increase more than the viscosity of ungelled or neat propellants. If MICOM GEL was used in a one gel system with ungelled or neat IRFNA as the oxidizer, (without a method of compensating for this inherent viscosity change) an oxidizer/fuel (O/F) shift would occur leading to poor combustion efficiency. In an attempt to overcome this viscosity induced O/F shift, a theoretical and experimental program was initiated at MICOM to evaluate a gelled oxidizer. The oxidizer chosen to evaluate was IRFNA which is a storable oxidizer and is usable throughout the environmental temperature range. It has been extensively used in the LANCE system and has passed all the rigorous environmental and handling tests demanded by this system without any problems. Gelling the oxidizer could result in an advantageous combination with a gelled fuel, such as MICOM GEL, particularly if the oxidizer could be gelled to contain a suspension of powdered ingredients in a uniform concentration. Gelling the oxidizer composition could maintain high Isp, increase density Isp and reduce the oxidizer/fuel shift caused by the difference in viscosity of the oxidizer and fuel.
Therefore, it is an object of this invention to provide a gelled thixotropic oxidizer.
Another object of this invention is to provide a gelled thixotropic oxidizer which has the ability with low gellant concentration to suspend added ingredients in a uniform concentration even when subjected to high-g forces.
A further object of this invention is to provide a gelled thexotropic oxidizer which eliminates or reduces the viscosity shift differences between the fuel and oxidizer while maintaining the safety, ease of pumping at zero gravity and high Isp and density impulse advantages of gels.